JP2623026B2 - Method for producing high-purity glassy carbon material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a glassy carbon material having a high-purity material structure.

[0002]

2. Description of the Related Art A glassy carbon material is a heterogeneous carbon material having a vitreous structure, and is widely used in various fields in various fields by utilizing its properties. Recently, it has been found that a homogeneous and dense non-contaminated material structure is suitable for a plasma etching electrode of a silicon wafer and a member for an ion implantation apparatus. The members used are required to have extremely high material purity.

[0003] Usually, a glassy carbon material is produced by a method in which an initial condensate of a phenol resin or a furfuryl alcohol resin is used as a raw material, a curing agent is added to the raw material, and the mixture is molded and cured, and then calcined and carbonized. In this production stage, impurities are mixed in from the raw material resin, the curing agent, the atmospheric gas at the time of calcination and the like, and the product purity is reduced. In particular, a sulfur-based compound such as paratoluenesulfonic acid, which is preferably used as a curing agent, causes a sulfur component to remain in the raw material resin and also remains as an impurity in the product.

However, it is extremely difficult to purify the impurities mixed into the glassy carbon structure in a post-treatment manner. In other words, as an effective means for purifying general carbon materials, a method of deashing with a halogen-based gas in a high temperature range of 2000 ° C. or higher is known, but glassy carbon materials are different from general carbon materials. On the contrary, since it has a very dense closed tissue, the dispersion of the demineralized gas into the tissue is hindered, and the diffusion and removal of impurities do not proceed smoothly. Moreover, it is almost impossible to expect the removal of sulfur components in this type of demineralization.

[0005]

As a result of a detailed study of the relationship between the properties of the raw material resin and the properties of the material after carbonization, which had not been clarified in the prior art, the present inventors have found that the range of the property properties is limited. Phenolic resin can be heat-cured smoothly without adding a third component such as a curing agent, and the fact that it is converted into a high-quality glassy carbon material while maintaining excellent purity was developed to develop the present invention. It has been reached.

Accordingly, an object of the present invention is to use a specific thermosetting phenol resin to which no curing agent is added as a raw material.
It is an object of the present invention to provide a method for efficiently producing a glassy carbon material having a homogeneous dense structure and excellent material purity by firing and carbonizing in a high-purity environment.

[0007]

In order to achieve the above object, a method for producing a high-purity glassy carbon material according to the present invention comprises a method for producing a high-purity glassy carbon material having a molecular weight of 100 or more, a viscosity of 1 to 100 poise, a gelation time of 5 to 60 minutes, and an ash content. It is characterized in that a phenol resin having a content of less than 5 ppm is used as a raw material, molded and heated and cured without adding a curing agent, and then calcined and carbonized in a high-purity non-oxidizing gas atmosphere.

The numerical values of the property characteristics in the above constitution are as follows: the molecular weight is the freezing point depression method using dioxane, the viscosity and the gelation time are JIS K6909-1977 “Testing method for liquid phenol resin”, and the ash content is JIS M8812-1976.
Each was measured by the "ash content determination method".

Among the raw material characteristics, the use of a phenol resin having a molecular weight of 100 or more is a necessary condition for obtaining a glassy carbon material having a high tissue strength. If the molecular weight is less than 100, the crosslinked structure after curing becomes weak. And it is not converted to high-strength carbide. If the viscosity is less than 1 poise, the strength of the structure after carbonization is reduced. If the viscosity exceeds 100 poise, volatilization of the condensed water does not proceed smoothly during curing and pores are frequently generated.
Therefore, the viscosity is set in the range of 1 to 100 poise.

The reason for using a property resin having a gelling time in the range of 5 to 60 minutes is that, in a usual liquid thermosetting phenol resin which gels in less than 5 minutes, the progress of curing is too rapid and unreacted substances or condensed water Is accumulated without volatilization, and a large amount of pores are generated.On the other hand, if the gelation time exceeds 60 minutes, a long time is required for the curing process, which hinders the industrial production side, and the curing process requires external sources. This is because a pollution phenomenon is likely to occur.

The use of a phenolic resin having an ash content of less than 5 ppm is an important requirement for producing a high-purity glassy carbon material. When the ash content is 5 ppm or more, it is contained in the tissue as an impurity during the carbonization process. So that high purity characteristics cannot be imparted.

The thermosetting phenol resin raw material used in the present invention is produced by a method in which high-purity phenol and formalin are subjected to a condensation reaction in a clean container in the presence of an alkali catalyst. At this time, phenol and formalin both have an ash content of less than 5 ppm, and urea-based basic substances such as ammonia, methylamine, diphenylamine and the like which volatilize and disappear during calcining and carbonization are applied as an alkali catalyst, and phenol / formalin is used. Composition ratio, temperature,
By adjusting the reaction conditions such as the amount of the catalyst and the time, a phenol resin having the above-mentioned properties can be synthesized.

The phenolic resin raw material is molded and heat-cured without adding any curing agent. In this case, since the raw material is in a liquid state, molding is performed by a cast molding method or a multiple molding (overcoating) method. However, in order to form into a shape such as a crucible or a pipe using a molding method or an extrusion molding method, a powdery phenol resin having an ash content of less than 5 ppm is blended with the above-mentioned liquid phenol resin as a raw material. Subjecting the kneaded material to a molding step is an effective process. In this case, as the powdery phenol resin to be blended in this case, one obtained by hardening and pulverizing the above-mentioned liquid phenol resin is suitably used. The curing process is performed in a temperature range of 150 to 250 ° C.

The cured molded body is then transferred to a heating furnace maintained in a non-oxidizing gas atmosphere and calcined and carbonized in a temperature range of 800 ° C. or more. As the non-oxidizing gas blown into the heating furnace, hydrogen, argon, nitrogen or the like having at least an impurity content of less than 10 ppm is used. The material after calcining and carbonization is graphitized at a temperature of 2000 ° C. or higher in a non-oxidizing gas atmosphere as described above, if necessary. These calcined carbonized or /
The graphitization may be carried out at normal pressure, but when carried out under reduced pressure, the evaporation of impurities is promoted, so that a better purification result is brought. In addition, in order to remove impurities based on external contamination, a demineralization treatment using a halogen-based gas can be performed as a post-treatment. Through these steps, a high-purity, high-quality glassy carbon material is produced.

[0015]

According to the present invention, a thermosetting phenol resin liquid having the property of converting into a high-purity, homogeneous and dense vitreous carbonized structure or a mixture of the resin liquid and a powdery high-purity phenol resin is used as a raw material. The carbonization treatment is performed selectively, without adding a curing agent as a source of impurity contamination, and in a heating environment free from contamination. By this raw material selection and non-contamination process, it becomes possible to always produce a glassy carbon material having high purity and high strength characteristics.

[0016]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 5 and Comparative Examples 1 to 5 Phenol, formalin and ammonia having an impurity content of 1 ppm or less were put into a three-necked flask, and the condensation reaction and the enrichment were advanced under the changed conditions to obtain the properties shown in Table 1. A phenol resin precondensate (liquid resin) having characteristics was prepared.

[0018]

Each phenolic resin liquid shown in Table 1 is used as a raw material, poured into a quartz vat (100 mm long, 50 mm high), placed in a vacuum desiccator, and evacuated at 10 torr for 1 hour to remove air bubbles remaining in the resin liquid. Removed. Then, it was transferred to an electric drier in an atmosphere from which dust was completely removed, and heat-cured at 180 ° C. for 1 hour to obtain a thin plate having a length and width of 90 mm and a thickness of 1.4 mm. This thin plate compact was sandwiched between high-purity graphite plates (G347SS, manufactured by Tokai Carbon Co., Ltd.) with impurities of less than 5 ppm,
Also high-purity graphite heater [G1 manufactured by Tokai Carbon Co., Ltd.
51ASS] in a packingless heating furnace [TP150, manufactured by Tokai High Heat Industry Co., Ltd.], and keeping the atmosphere in the furnace at 10 ° C while maintaining the atmosphere with high-purity argon gas containing less than 10 ppm of impurities.
By heating to 2000 ° C. at a heating rate of / hr to perform a carbonization treatment, a thin glassy carbon material having a length and width of 70 mm and a thickness of 1 mm was produced. The impurity content and various characteristics of each glassy carbon material thus manufactured were measured, and the results are shown in Table 2.

[0020]

From the results shown in Table 1, each of the glassy carbon materials produced in Examples 1 to 5 had a low ash content and a low sulfur content of less than 10 ppm, and also had a high level of bulk density and strength characteristics. On the other hand, in Comparative Example 1 in which the gelling time of the raw material resin is less than 5 minutes, many pores are generated and the bulk density and the bending strength are reduced, and in Comparative Example 2 in which the gelling time exceeds 60 minutes, impurities are contained. The amount is increasing. Since the raw material resin of Comparative Example 3 has a molecular weight of less than 100, strength and hardness are reduced. In Comparative Examples 4 and 5 of the raw resin whose viscosity is out of the range of 1 to 100 poise, it is recognized that the bending strength is low.

Example 6 A thin plate formed and cured by the same process as the phenolic resin raw material of Example 2 was placed in a firing furnace filled with ordinary coke packing, and fired and carbonized to 2000 ° C. The obtained glassy carbon material has an ash content of 21 ppm, a sulfur content of 50 ppm, a bulk density of 1.50 g / cc, and a specific electric resistance of 50 × 10 ⁻⁴ Ωc.
m, bending strength 1310 kgf / cm ² , hardness 101, and extremely poor purity.

Example 7 A liquid phenolic resin having a molecular weight of 150, a viscosity of 150 poise, a gelling time of 40 minutes and an ash content of less than 5 ppm, and a powdery phenolic resin obtained by curing the liquid resin and pulverizing it to an average particle size of 9 μm were used. 1: 1 and thoroughly kneaded using a cleaned agate mortar. The kneaded material was filled in a mold made of high-purity graphite and formed into a crucible having an outer diameter of 50 mm, an inner diameter of 40 mm and a height of 50 mm under the conditions of a heating temperature of 150 ° C. and a pressure of 5 kg / cm ² . Next, the crucible compact was placed in the same packingless heating furnace as in Example 1 and subjected to a calcination treatment under the same conditions.
The obtained crucible-shaped glassy carbon material has an ash content of 3 pp.
m, sulfur content 5ppm, bulk density 1.51g / cc, specific electric resistance 51x
It exhibited characteristics of 10 ⁻⁴ Ωcm, bending strength of 1310 kgf / cm ² , and hardness of 100, and was confirmed to have a dense structure with high purity and high strength.

[0024]

As described above, according to the present invention, a phenol resin having specific properties is used as a raw material, and a non-staining heat treatment step is performed without using a curing agent.
By performing calcination, the ash and sulfur content are reduced.
It is possible to efficiently produce a glassy carbon material having a high-purity of less than 10 ppm and a homogeneous dense structure having excellent strength properties. Therefore, it is extremely useful as a manufacturing technique of a member for a semiconductor field requiring high purity and high material properties.

Claims (2)

(57) [Claims] (1) a molecular weight of 100 or more, a viscosity of 1 to 100 poise,
A phenolic resin with a gelation time of 5 to 60 minutes and an ash content of less than 5 ppm is used as a raw material, and is molded and heated and cured without adding a curing agent, and then calcined in a high-purity non-oxidizing gas atmosphere. Characteristic method for producing high-purity glassy carbon material. 2. The method for producing a high-purity glassy carbon material according to claim 1, wherein the phenol resin according to claim 1 is mixed with a powdery phenol resin having an ash content of less than 5 ppm as a raw material.